1. Field of the Invention
In a first aspect thereof, the present invention relates to a safety support intended for being mounted on a rim of a vehicle wheel within a tire, for supporting said tire in case of pressure loss.
The present invention also relates to a safety system for vehicle tires comprising the above-mentioned safety support and a tire having a tread, a couple of sidewalls and a couple of beads suitable for being mounted on respective housing seats of a rim.
Lastly, the present invention relates to a vehicle wheel comprising a tire, a rim and the above-mentioned safety support.
2. Description of the Related Art
In the field of the production of vehicle tires the need has always been felt of ensuring a safe running condition for the vehicle also in case a tire of said vehicle loses its pressure.
To this purpose, safety supports have been made intended for being mounted on the rim within the tire, which safety supports support said tire, and particularly the crown portion of the same, should the tire pressure markedly reduce with respect to the tire nominal pressure.
With regard to this, a method for evaluating the compliance of the tire with the above-mentioned safety need may consist, for instance, in testing the tire performance in the so-called “run-flat” conditions. In the present description and in the subsequent claims, the expression “testing the tire performance in run-flat conditions”, is used to indicate a test methodology developed by the Applicant, by which a vehicle must run for about 200 km at a speed of 80 km/h, with a load equal to 80% of the maximum load (Load Index) admitted for the tire.
It is particularly difficult to satisfy entirely the above-mentioned safety need without causing a substantial increase in the total weight of the wheel wherein the safety support is inserted, with an ensuing increase in non-suspended masses and a corresponding worsening of the vehicle performance.
A further difficulty is that of providing the safety support with an adequate centrifugation resistance, both in terms of structural integrity of the support also at high speed, and in terms of maintaining a stable contact between the support and the rim, in the so-called normal running conditions, i.e. at the nominal pressure of the tire.
The structural integrity of the safety support may be tested, for example, by rotating the rim-safety support assembly at a rotation speed equivalent to a supposable vehicle running speed in the order of 400 km/h.
A further difficulty in the manufacture of a safety support having a good quality lies in ensuring an adequate contact surface between the tread and the rolling surface when, due to a loss of the tire pressure, the safety support gets in touch with the tire and supports the latter. In other words, the safety support should be capable of deforming so as to adhere as much as possible to the tire.
Until now, the attempts carried out in the art aiming at satisfying the above-mentioned need in all its aspects, i.e. the attempts to achieve an adequate performance in the “run-flat” conditions by means of a safety support which has a limited weight while being resistant to centrifugation and such as to maximize the contact surface between the tread and the rolling surface, have not given a fully satisfactory result, involving a more or less evident worsening of one or more of the characteristics described above.
For instance, patent application EP 0 796 747 discloses a safety support inserted in a tire, made of a soft elastomeric material, said support comprising an annular base reinforced by a circumferential reinforcing layer, an annular top provided in its radially outer wall with longitudinal grooves, and an annular body connecting the base with the top.
In case of loss of the tire pressure, even though the support proposed by patent application EP 0 796 747 allows to obtain both an adequate contact between the support and the crown portion of the tire—thanks to the deformability of the elastomeric material used—and an adequate centrifugation resistance—thanks to the introduction of the circumferential reinforcing layer embedded in the elastomeric material—the manufacture of the support is rather complex and the total weight of the wheel is excessive with respect to the weight of a traditional wheel having no safety support.
U.S. Pat. No. 4,751,951 discloses an annular safety support of elastomeric material in the form of a foam provided with closed cells containing gas under pressure. In order to control the expansion of said safety support and to maintain the same in position between the beads of the tire when the latter is deflated, the safety support is enveloped by a layer of reinforcing cords, fact which requires several cumbersome handling and assembling operations, similar to those required in the manufacture of a tire. Besides, according to what has been said above with reference to patent application EP 0 796 747, the desired maintenance of the support in position, i.e. the maintenance of a stable contact between the support and the rim, is accomplished to the detriment of the wheel weight, which increases too much with respect to the weight of a traditional wheel having no safety support.